Our overall goal is twofold: to prevent the further spread of HIV among injection drug users (IDUs) and their families in Guangxi Province, China and to gain insight into effective strategies for vaccine development in this high risk population. Guangxi Province is the area in China with the highest rate of injection drug use; at the same time, HIV-1 infection is emerging there as a significant health problem. This population offers the unique opportunity to determine the distribution and transmission patterns of several different HIV-1 subtypes in a population that abuses only one drug--heroin-- but in whom multiple subtypes of HIV-1 are spreading. There will be four specific aims (1) to estimate the prevalence of HIV-1 infection and to identify risk factors for prevalent HIV-1 infection; (2) to document the prevalence and distribution of different subtypes of HIV-1; (3) to estimate the incidence of HIV-1 infection and document risk factor profiles over time among heroin users; (4) to document changes in risk factor profiles over time among HIV negative, and HIV positive heroin users, including seroconvertors; (5) to determine the subtypes of HIV-1 in seroconvertors and to compare the relative transmissibility of different subtypes of HIV-1. These aims will be carried out in Guangxi Province through a longitudinal investigation of 600 drug users about whom demographic, social, and drug use information will be collected and analyzed.